This application requests five years of continued support for an ongoing, multidisciplinary program of research on autism and related developmental disorders. The proposed work represents the evolution of the program project reflecting an increased focus on autism and related disorders. This application builds on important resources and research programs available at Yale. The broad theme that unifies this research program is the focus on understanding mechanisms of dysfunction in autism, and related conditions as they relate to development and outcome. The focus of the grant is on integrating advances in neuropsychology, developmental psychopathology, neuroscience and genetics into understanding the clinical manifestations, which in turn are studied in relation to specific neurodevelopmental processes and risk factors. Objectives include: 1) elucidating the earliest manifestations of autism from birth to 2 years through the prospective study of a large cohort of infants with a sibling who has autism;2) identifying predictors of outcome and clarify phenotypic variation in autism in a large group of school aged children, who were originally diagnosed with a pervasive developmental disorder at 2 years of age using a longitudinal design that will map trajectories across multiple domains of development;3) clarifying mechanisms in the development and expression of conversational pragmatics and prosody in high functioning individuals with ASD through studies using emerging technologies to examine conversational behaviors in greater depth and lay the foundation for developmental measures that can be used in clinical settings. In addition to these three projects three core resources are proposed and include: A) Administrative, B) Assessment C) Statistics &Research Design. This application brings together existing and new expertise, infrastructure and resources focused on diagnosis, early detection, causes, and treatment of autism. The work proposed is highly interdisciplinary drawing on both basic and clinical sciences and innovative research designs and state-of-the-art technologies. This work brings together, behavioral, biomedical, and clinical science investigators into a transdisciplinary program of research on autism.